This invention relates to a novel zeolite and to a novel process for its preparation. In particular, the zeolite has a structure which may be stoichiometric quantities such that the ratio of product to reactants approaches unity.
A zeolite designated as zeolite L is known to exhibit good catalytic properties, particularly for hydrocarbon conversion, and advantageous sorbent properties as described, for example, by Barrer et al., Surface Science, 12, 341 (1968). The chemical composition of zeolite L is disclosed in U.S. Pat. No. 3,216,789 to be: EQU 0.9-1.3 (M.sub.2/n):Al.sub.2 O.sub.3 :5.2 to 6.9 SiO.sub.2 :xH.sub.2 O
where M is an exchangeable cation of valence n and x is from 0 to 9. Zeolite L also has a characteristic x-ray diffraction pattern, and its structure has been determined by Barrer et al., Zeit. Krist., 128, 352 (1969). The x-ray diffraction pattern of zeolite L has the following more significant d(.ANG.) values:
16.1.+-.0.3
7.52.+-.0.04
6.00.+-.0.04
4.57.+-.0.04
4.35.+-.0.04
3.91.+-.0.02
3.47.+-.0.02
3.28.+-.0.02
3.17.+-.0.01
3.07.+-.0.01
2.91.+-.0.01
2.65.+-.0.01
2.46.+-.0.01
2.42.+-.0.01
2.19.+-.0.01
A typical preparation of Zeolite L as disclosed by Breck, Zeolite Molecular Sieves, New York: J. Wiley, 283 (1974), employs an excess of SiO.sub.2 and a greater excess of K.sub.2 O.
The preparation of zeolite L described in U.S. Pat. No. 3,216,789 involves crystallizing the zeolite from a reaction mixture having a mole ratio of silica to alumina which is significantly higher than the ratio in the formed zeolite. Specifically, the reaction mixture comprises mole ratios:
______________________________________ K.sub.2 O/(K.sub.2 O + Na.sub.2 O) 0.33-1 (K.sub.2 O + Na.sub.2 O)/SiO.sub.2 0.35-0.5 SiO.sub.2 /Al.sub.2 O.sub.3 10-28 H.sub.2 O/(K.sub.2 O + Na.sub.2 O) 15-41 ______________________________________
Zeolite L and zeolites having related structures belong to the "L" family of zeolites. This family is characterized by having a 12-ring hexagonal structure with pore dimensions of about 5.5 to 7.2 .ANG.. In addition to zeolite L there are also barium zeolites Ba-G and Ba-G,L described by Barrer et al. in J. Chem. Soc., 2296 (1964), J. Chem. Soc., 1254 (1972) and J. Chem. Soc., 934 (1974); Linde omega disclosed in U.S. Pat. No. 4,241,036; zeolite ZSM-4 disclosed in U.K. Patent No. 1,117,568; and the mineral mazzite which occurs in nature (see Galli et al., Contrib. Mineral and Petrologie, 45, 99 (1974)). ZSM-10 (U.S. Pat. No. 3,692,470) may be a Dabco containing member of this group of zeolites. Similarly, zeolite UJ (U.S. Pat. No. 3,298,780) may also be of the zeolite L type.
Structures have been proposed for zeolite L (Barrer et al., Zeit. Krist., 128, 352 (1969)), Linde omega (Barrer et al., Chem. Comm., 659 (1969)), and mazzite (Galli, Crystal. Str. Comm., 339 (1974)). Galli et al., Contrib. Min. & Petr., 45, 99 (1974) have compared the data for zeolite L, omega and mazzite. Meier et al., Atlas of Zeolite Structures (1978) propose that mazzite, ZSM-4 and omega are isostructural, differing only in Si/Al ratios and cation contents. If all cation positions in L are filled by monovalent cations, L will have a minimum Si/Al ratio of 1.8 according to Baerlocher et al., Zeit. Krist., 136, 253 (1972).
British Patent No. 1,202,511 describes a revised zeolite L preparation using lower proportions of silica in the reaction mixture which comprises mole ratios of reactants as follows:
______________________________________ K.sub.2 O/(K.sub.2 O + Na.sub.2 O) 0.7-1 (K.sub.2 O + Na.sub.2 O)/SiO.sub.2 0.23-0.35 SiO.sub.2 /Al.sub.2 O.sub.3 6.7-9.5 H.sub.2 O/(K.sub.2 O + Na.sub.2 O) 10.5-50 ______________________________________
The ratio H.sub.2 O/(K.sub.2 O+Na.sub.2 O+SiO.sub.2 +Al.sub.2 O.sub.3) is preferably not greater than 6 to give a "dry gel" as product. The source of silica employed is a solid, amorphous silica.
U.S. Pat. No. 3,867,512 discloses a preparation of zeolite L from a reaction mixture having a molar composition:
______________________________________ K.sub.2 O/(K.sub.2 O + Na.sub.2 O) 0.3-1 (K.sub.2 O + Na.sub.2 O)/SiO.sub.2 0.3-0.6 SiO.sub.2 /Al.sub.2 O.sub.3 10-40 H.sub.2 O/(K.sub.2 O + Na.sub.2 O) 15-140 ______________________________________
in which the silica source is a gel having at least 4.5 weight percent water and prepared in a particular manner.
L. Wilkosz in Pr Chem 409 (1974) -Chemical Abstracts, 90 (1979) 573478 describes the preparation of zeolite L from a synthesis sol prepared by treating a solution containing silica, potassium hydroxide and sodium hydroxide with a second solution containing potassium aluminate, potassium hydroxide and sodium hydroxide and crystallizing for 72 hours at 20.degree. C. and 122 hours at 100.degree. C. The zeolite L product has a SiO.sub.2 :Al.sub.2 O.sub.3 ratio of 6.4:1, derived from input stoichiometries having SiO.sub.2 /Al.sub.2 O.sub.3 ratios between 15 and 30.
G. V. Tsitsishvilli et al. in Doklady Akademii NaikSSSR, 243, 438-440 (1978) describe the synthesis of zeolite L from alumina-silica gels containing tributylamine. The gels used had the following molar ratios:
______________________________________ SiO.sub.2 :Al.sub.2 O.sub.3 25 (K.sub.2 O + Na.sub.2 O):Al.sub.2 O.sub.3 18 (K.sub.2 O + Na.sub.2 O)/SiO.sub.2 0.72 H.sub.2 O/(K.sub.2 O + Na.sub.2 O) 20 K.sub.2 O:Na.sub.2 O 0.5 ______________________________________
Y. Nishiimura in Nippon Kagaku Zasshi, 91, 1046-9 (1970) describes in general terms zeolite L preparation from a synthesis mixture containing colloidal silica, potassium aluminate and potassium hydroxide having a SiO.sub.2 :Al.sub.2 O.sub.3 ratio of 15-25, but exemplifies only two synthesis mixtures having the following ratios of components: EQU 7K.sub.2 O:Al.sub.2 O.sub.3 :2OSiO.sub.2 :45OH.sub.2 O; and 8K.sub.2 O:Al.sub.2 O.sub.3 :10SiO.sub.2 :500H.sub.2 O.
U.S. Pat. No. 3,298,780 describes zeolite UJ having a composition, expressed as mole ratios of oxides, corresponding to EQU 0.9.+-.0.2R.sub.2 /.sub.v O:Al.sub.2 O.sub.3 :5.0.+-.1.5SiO.sub.2 :wH.sub.2 O
wherein R represents at least one cation having a valence of not more than 4, v represents the valence of R and w can be any value up to about 5, said zeolite having an X-ray powder diffraction pattern essentially as shown in the following table:
______________________________________ Interplanar Relative spacing, d(.ANG.) Intensity ______________________________________ 16.25 .+-. 0.25 VS 7.55 .+-. 0.15 M 6.50 .+-. 0.10 M 5.91 .+-. 0.10 W 4.61 .+-. 0.05 S 3.93 .+-. 0.05 S 3.67 .+-. 0.05 W 3.49 .+-. 0.05 M 3.29 .+-. 0.05 W 3.19 .+-. 0.05 M 3.07 .+-. 0.05 M 2.92 .+-. 0.05 M 2.66 .+-. 0.05 W ______________________________________
prepared by a process comprising preparing an aqueous reactant solution having a composition, expressed as mole ratios of oxides, corresponding to
______________________________________ SiO.sub.2 /Al.sub.2 O.sub.3 of from 6 to 30, R.sub.2/v O/SiO.sub.2 of from 0.30 to 0.70, and H.sub.2 O/R.sub.2/v O of from 80 to 140; ______________________________________
and maintaining said reactant solution at a temperature between 150.degree. F. (65.6.degree. C.) and 325.degree. F. (162.8.degree. C.) until the zeolite crystals are formed. Zeolite UJ is described as having nearly cubic shaped crystals with a crystal size ranging upward from 0.05 micron.
GB No. 1,393,365 describes zeolite AGl, related to zeolite L, having the molar composition other than water: EQU 1.05.+-.0.3M.sub.2 O:Al.sub.2 O.sub.3 :4.0-7.5SiO.sub.2
wherein M is potassium or a mixture of potassium and sodium, a characteristic x-ray powder diffraction pattern, and being capable of adsorbing at least 3% w/w perfluorotributylamine. As the zeolite L pore structure is too small to allow penetration by this molecule, zeolite AG-1 cannot be a highly pure zeolite L.
It was subsequently found that zeolite L may be used as a catalyst base in aromatization reactions. U.S. Pat. No. 4,104,320 discloses dehydrocyclization of aliphatic compounds in the presence of hydrogen using a catalyst comprising zeolite L and a group VIII metal, in which the zeolite L is of the formula: EQU M.sub.9/n (AlO.sub.2).sub.9 (SiO.sub.2).sub.27
(where M is a cation of valence n), but the silica to alumina ratio may vary from 5 to 7.
East German Patent No. 88,789 discloses dehydrocyclization using a catalyst formed from a zeolite precursor with a silica to alumina ratio of 5 or greater which is dealuminised to give a silica to alumina ratio of up to 70. Zeolite L is mentioned as a precursor.
European Patent Application Publication No. 40119 discloses a dehydrocyclization process operating at low pressure (1 to 7 bars) or low H.sub.2 /hydrocarbon ratio using a catalyst comprising platinum on a potassium zeolite L. Belg. Patent No. 888,365 describes dehydrocycliZation using a catalyst comprising platinum, rhenium (incorporated in the form of its carbonyl) and sulPhur to give an atomic ratio of sulphur to platinum of 0.05 to 0.6 on a zeolitic crystalline aluminosilicate base such as zeolite L. Belg. Patent No. 792,608 discloses the treatment of Zeolite L for use as a catalyst in isomerization by exchange with ammonium and chromium ions.